Intercommunicating telephone system



Aug. '31, 1948.

K. W. GRAYBILL INTERCOMMUNIGATING TELEPHONE SYSTEM Filed March 10, 1945 INVENTOR. v EN NETH W. GRAYBILL ATTORNEY Patented Aug. 31, 1948 INTERCOMIMUNICATING TELEPHONE SYSTEM KennethW.1Graybill, Elmhurst, Ill., assignor to Automatic Electric Laboratories, Inc., Chicago, 111., a corporation of Delaware -Application"March10, 1945, Serial No. 582,045

:1 *The present invention relates in general to intercommunicating telephone systems and, in

particular, to systems of the common-talkselective-signaling'type wherein impulse controlled means are employed for selectively connecting certain of the stations to a common talking circuit or for I selectively signaling certain ofthe stations.

'The principal'object of the present invention is 'to provide a simplejandeconomical system of the above character wherein separate channels are provided for transmitting speech signals in opposite directionsbetween two connected stations whereby the-transmission efficiency is raised so as to permit the use of loudspeaking equipment at one, or both, of two conne-cted stations.

A further object of the invention v isto -provide an intercommunicating system including master stations and subordinate stations'in which-means are'provi'ded for selectively establishing commu- 'nication between any master-stationand any subordinate station. or anyother' master station,

under the control of animpulsing devi-ce at *a "calling masterstation and in which circuit arrangements are provided for enabling any of the subordinate stations "to selectively signal *the "master stations and to establish communication between a calling subordinate station-and a called master "station in response to an answer by the called master station. *In the illustratedembo'di- -ment of theinvention the subordinate stations selectively signal the masterstations by -'co'de signals.

- Other obj ects or the invention will appear upon a further perusal of J the specification taken in conjunction with the accompanying-drawing,

- which illustrates diagrammatically the apparatus and circuits involved in l a '--system-embodyingthe of counting chain'relayseach correspondingto one of 'thestati-ons, apair of impulsing' relays for each-master station and two common relays. If 'desired, both themaster and the subordinatestations "may 'be {equipped with loudspeaking re- "ceivers provided that close=talking transmitters are alsor'use'd at thelsubordinate stations. IiEach :stationris connectedto the relay switching-1 equip- "lment by three'fcondu'ctors. :A. ground connection is also illustrated at eachstation and at "the vswitching point. This istchiefly forconvenience in drawing for it is usually preferable toemploy a fourth conductor between each stationandthe switching point in place of the ground connections. One of these three conductors and'ground, or oneo'f these three :conductors and a fourth conductor, defines a channel fortransmitting speech signals from each station, 'andarsecond one ofthese three conductors and ground, "or a second one of these three conductors :and the fourth-conductor, defines a channelzfor receiving speech signals at each station. The third conductor and ground, or thethirdand fourth :conduct-ors,-is used iorsignaling. can of the relays are located at a central switchingpointzorexchange. The first two conductors of-eachmaster station are normally connectedto a :pair ofrcom- 'mon leads bytheir corresponding-counting relays. These leads are ..norrnally disconnected from each station equipment by the .hookswitch 'thereat. Thefirst two conductors of each subordinate station are permanently connected to the station equipment but are normally :disconnected 'from sai'd common leads Ibyttheircorresponding counting relays.

When a master station calls a subordinate station; the transmitter andv receiverzat the master station-are connected tosaid common leadsl'by the'ho'ok switch atthe master station. The:;impulsing device at the master station "is i then operated to cause the counting relays to be Ioperated successively until thedesired subordinate station is 'connectedto said common leads, whereupon :conversation may take p1ace betWeen the connected stations. When one master station calls a second master station the connections of the first twoconductors of the second master station to the common leadsare reversed when-its correspondin counting relay operates so that the transmitter of each of the connected. stations willbe connected to the receiver of the other sta- "tion when the call is answered. The counting "relay I operated also energizes the buzzer at- 'the called master station over its third conductor and-grounduntil the call is answered.

-s'ubordinate station rmay call a maste-r station by operation ofzthe push button thereat in accordance with a-predetermined code. This causes the counting relay corresponding -tothe calling subordinate station to .be intermittently k operated :over. the third conductorofthe calling station :to connect. itto the' common leads rand ito operate the buzzers eat-all of the F master stations inPaccordancewith the predetermined code. This counting relay is maintained operated under the control of the called master station when the call is answered.

Referring now to the drawing, the stations designated A, B, and C are master stations and the stations designated D and E are subordinate stations. As previously mentioned, each master station comprises a conventional telephone transmitter l and receiver 2, a hook or cradle switch 3, a buzzer 4, and an impulsing device 5, which device may simply be a normally closed circuit push button or may be the usual telephone dial. Each subordinate station comprises a loudspeaking transmitter 6 and receiver 1, and a push button 8. The switching equipment comprises a group of counting chain relays F to K; a pair of imj pulsing relays for each station consisting of line relays L, N, and R, and slow release relays M, P, and S; and two common relays T and U. It is believed that the operation of the system will best be understood by a detailed description of the manner in which typical types of connections are established.

Master station to subordinate station call Assume that a party at master station A desires to communicate with another party at subordinate station D. The handset, in which transmitter l and receiver 2 are mounted, at station A is lifted from the hookswitch 3 which completes a circuit from ground through transmitter I, impulsing device 5, contacts of the hookswitch, and over conductor 2| to battery in series with on its core. Relay J connects the receiver 1 at station D to conductor 9 at contacts J3, and connects the transmitter 6 at station D to battery in series with relay U at contacts J2. Relay U operates and connects the transmitter 6 to conductor ID in series with condenser l I. A two way conversation over separate oppositely directed channels may novi take place between stations A and D, the party at station A speaking into transmitter I thereat causes corresponding speech currents to be transmitted over conductor 2!, through condenser l2, and over conductor 9 to the receiver 1 at station D, which currents return'over ground or an equivalent common conductor. Similarly, the party at station D speaking into transmitter 6 thereat causes correspondrelay L. The hookswitch also connects the re-..

ceiver 2 to conductor 22 and disconnects buzzer 4 from conductor 23. Relay L operates over the above traced circuit and closes a circuit from ground through contacts Ll, relay M, contacts M3, and contacts T4 to battery. Relay M oper-' ates, prepares a locking circuit for counting relays F to K at contacts Ml, closes a holding circuit and opens its operating circuit at contacts M3, and closes a circuit to relay T at contacts M4.

Relay T operates and disconnects battery from relays P and S at contacts T4. The impulsing device 5 at station A is now operated to momentarily interrupt the circuit to relay L a number of times corresponding to the call number of the desired station, which number is ,two in the present instance. The first restoration of relay L closes a circuit to the upper winding of relay K fromground through contacts LI, M2, F6, G6, H6, J 6, and K6. Each of the counting relays is margined so as to close only its preliminary contacts, which are numbered 4, when the circuit to its upper winding is closed. Consequently relay K closes only contacts K4 which connect its lower winding to ground at contacts Ml through contacts J5, H5, G5, and F5. The lower winding of relay K is thus short-circuited until relay L reoperates at which time the two windings of relay K are energized in series causing it to operate all of its contacts. Contacts K6 transfer the impulsing lead from relay K to relay J. The

closure of contacts Kl is without efiect at this time since contacts Tl are open. The second restoration and reoperation of relay L causes relay J to be operated in two steps just as relay K was operated. When relay J operates completely it opens the lockin circuit for relay K at contacts J5 causing relay K to restore. Since relay L remains operated following its second reoperation, relays M, T, and J will remain operated. Relay M is maintained operated during the momentary restorations of relay L due to the copper sleeve ing speech currents to be transmitted through condenser II and over conductors l0 and 22 to the receiver 2 at station A, which currents return over ground or an equivalent common conductor. An impedance matching transformer is employed with each of the loudspeaking receivers l in order to secure the maximum output therefrom. When the conversation is completed the handset is replaced on hookswitch 3 at station A thus opening the circuit to relay L. Relay L restores, opens the circuit to relay M andcloses a circuit to the upper winding of relay H through contacts M2, F6, G5, H6, and J6. Relay H operates its preliminary contacts H4. Relay M restores, opens the operating circuit to relay H at contacts M2, opens the locking circuits to relays H and J at contacts MI, and opens the circuit to relay T at contacts M4. Relays H, J, and T restore.

Master station to master station call Assuming now that the party at master station A desires to speak to a party at master station C instead of to a party at subordinate station D, the operations are identical to those previously described except that the circuit to relay L is momentarily interrupted three times instead of twice. Consequently relay H will be operated completely after the third reoperation of relay L. When relay H operates completely it opens the locking circuit to relay J at contacts H5, reverses the connections between the common conductors 9 and Ill and the conductors 24 and 25 extending therefrom to station C at contacts H2 and H3, and closes a circuit to the buzzer 4 at station C over lead 26 at contacts HI. Buzzer 4 operates to signal the party at station C. When the call is answered by lifting the handset from the hookswitch 3 at station C a circuit is completed to relay R over conductor 24 in series with transmitter l. Relay R operates without effect since the operating circuit for relay S is open at contacts T4 of relay T, which is maintained operated by relay M. The function of relay R is simply to furnish transmission battery to the transmitter at station C when that station is the called station. Operation of the hookswitch 3 at station C also opens the circuit to buzzer 4 thereat and connects receiver 2 to-thecommon conductor 9 over conductor 25 and through contacts H2. A two way conversation over separate oppositely directed channels may now take place between stations A and C. The party at station A speaking into transmitter l thereat causes corresponding speech currents to be transmitted over conductor 2|, through condenser 12, 'over common conductor 9, through contacts H2, and over conductor 25 toreceiver 2 at station C, which currents return over ground or an equivalent cominon conductor. Similarly, the party :at station C'speaking into the transmitterl thereat causes corresponding speech .currents to be transmitted over conductor 24, through condenser 21 and contacts H3, over commonconductor 'I D: and conductor 22 to the receiver 2 at station A, which currents are returned over ground or an equivalent common conductor. When the conversation is completed both parties restoretheir handsets on the hookswitches opening the circuits to relays L and R. Relay R restores. Relay L restores, closes a circuit to the upper winding of relay .G through contacts M2, F6, G6, andLI-IB and opens the circuit to relay Mat contacts Ll. Relay G operates its preliminary contacts G4. Relay B restores, opens the operating circuit to "relay G at contacts M2, opens the locking circuits to relays G and H at contacts MI, and opens the circuit to relay Tat contacts M4. Relays .G, H, and T restore.

Subordinate station to master station call Assuming that a party at subordinate station D desires to converse with a party at master station A, the push button 8 at station D will be momentarily operated a number of times according to a predetermined code after which it will be held operated continuously until the call is answered. 'When this push button is operated it closes acircuit from ground over conductor-28, through contacts T3, and through both windings of relay J to battery. Relay J operates completely each time the above circuit is closed and closes a circuit to the buzzers 4 at all of the master stations from battery through contacts J I, Tl, over common lead 29, and over individual station leads such as 23 to ground through the buzzers at each station. The operation of relay J also causes relay U to operate in series with transmitter 6 but without effect at the moment. Since the code transmitted is characteristicoi station A, only a party at that station Will respond. When the handset at station A is lifted from the hookswitch thereat rela L is operated over a previously traced circuit. Relay L in operating brings about the operation of relays Mand T as previously described. When relay M operates it closes the locking circuit to relay J from ground through contacts M I, F5, G5, H5, and J4. Prior to the closure of this locking circuit, relay J is held operated over conductor 28 bypush button 8. When relay '1. operates it opens the operating circuit to relay J at contacts T3 and disconnects battery through. contacts J I; from common lead 29 at contacts TI to prevent further operation of the buzzers at stations Band C. The connection thus established is identical to that which resulted when station D was called by station A. When the party at station D hears the party at station A reply to the call he may release push button 8. The speech currents are transmitted over the same paths as previously traced and the release of the switching relays is effected as previously described when the handset at station A is restored on the hookswitch thereat. It should be noted that in the event that a callwas being placed, or had been completed, by a master station at the time that the party at station D operated push button 8, relay T being operated would prevent the operation of relay J since the connection between this relay and conductor 28 would be open at contacts T3, thereby preventing interference with the previously initiated, or established, connection.

Although the invention has been illustrated by 6 a particular embodiment thereof, it sh'ouldtbe'apparent that numerous modificationsmay be made therein without departing from the truespirit and scope of=the invention as defined'in the subjoined claims.

What is claimed is:

1. Inatelephonesystem, a plurality of telephone stations each including an impulsing device, a central station,lines extending from said central station to each of said first stations, each of said lines definingindependent incomingand outgoing signal current channels, each incoming channel normally connected to the correspon'ding incoming channelof all other of said lines and each outgoing channel normally -'-connected to thecorresponding outgoing channel of said other lines, and "switching means at'said central station operative under thecontrol'of the impulsing device at any "one of said first'stations-over the line extendingthereto to associate the incoming channel of said one line with the outgoing channel of another one of said lines 'and'tofassociate the outgoing channel of said one line with the'incoming channel or said other one of said lines.

2. A telephone'systemas claimed in claim "1 "in which'said switching means comprisesa chain of counting relays, each corresponding to one tof said first stations.

3. In a telephone system, a plurality of telephone stations each including "an impulsing 'device, a central station, lines extending therefrom to each of said first'stations, a pair of relays corresponding to each of .saidfirst stations and a common selecting'means in the central station, thefirst relay of any one of said pairs being connected in series with the impulsing device atits corresponding station over the line extending thereto in response to the initiation of a call thereat, the second relay 'of said one'pair operative in response to the operation of said first relay to associate said common selectingmeans With said first relay, said common selecting means being directively operated in response to intermittent operation of said first relay associated therewith under the control of the impulsing device at the calling station to extend a connection therefrom to'a called one of said'stations, and circuit arrangements for individually furnishing transmission'b'attery to the calling and called stations through the first relays of the corresponding pairs.

4. In a telephone systerrna plurality of telephone stations, a central station, lines extending from said central station to each of saidfirst stations, each of said lines including a'firstconductor over which signal currents are attime's transmitted and a second conductor 'over'which signal currents are at times received at thecorresponding one of said first stations, "switching means at said central station normally connecting the transmitting and receiving conductors of all of said lines to a'pair of commonconductors in like manner, said switchingrneans being operative under the control of any of said first stations toreverse the connections between the pair of common conductors and the transmitting and receiving conductors of the'line extending to any other one of said first stations "whereby two way communication between any two of said first stations may be effected over separate and oppositely directed channels.

5. In an intercommunicating system, a plurality of stations each having transmitting and recalving means; each of said stations having separate transmitting and receiving circuits at times associated with the transmitting and receiving means thereat, conductors common to said stations, the transmitting and receiving circuits of all of said stations being normally connected to said common conductors in like manner, and means operative .by a calling one of said stations to reverse the connections between said common conductors and the transmitting and receiving circuits of a called one of said stations whereby two way communication between any two of said stations may be effected over separate and oppositely directed channels.

6. In an intercommunicating system, a plurality of stations each having transmitting and receiving means, each of said stations having separate transmitting and receiving circuits at times associated with the transmitting and receiving means thereat, conductors common to all of said stations, the transmitting and receiving circuits of all of said stations being normally connected to said-common conductors in like manner, and means operated when a call is extended between any two of said stations to reverse the connections between said common conductors and the transmitting and receiving circuits of one of said two stations whereby two way communication is effected therebetween over separate and oppositely directed channels.

'7. In an intercommunicating system, a plurality of master stations each including an impulsing device and a signal device, a plurality of subordinate stations each including a switch, a central station, lines extending from each of said master stations and each of said sub-ordinate stations to said central station, switching means at said central station operative under the control of the impulsing device at a calling one of said master stations to selectively connect said one master station in communicative relationship with any of said subordinate stations, switching means operative under the control of the switch at a calling one of said subordinate stations to operate the signal devices at all of said master stations simultaneously, the desired master station being designated by a predetermined code, the response by the desired master station connecting it in communicative relationship with said one calling subordinate station.

8. In an intercommunicating system, a plurality of master stations each including a signal device, a plurality of subordinate stations, a central station, lines extending from each of said master stations and each of said subordinate stations to said central station, switching means at said central station operative under the control of a calling one of said master stationsto selectively connect it in communicative relationship with any of said subordinate stations, switching means operative under the control of a calling one of said subordinate stations to operate the signal devices at all of said master stations simultaneously, the desired master station being designated by a predetermined code, said switching means including means responsive to an answer by the desired master station for preventing further operation of said signal devices.

9. In an intercommunicating system, a plurality of master stations each including a signal de vice, a plurality of subordinate stations, a central station, lines extending from each of said master stations and each of said subordinate stations to said central station, switching means at said central station operative under the control of a calling one of said master stations to selectively connect it in communicative relationship with any of said subordinate stations, switching means operative under the control of a calling one of said subordinate stations to operate the signal devices at all of said master stations simultaneously, and means preventing operation of said signal devices by a subordinate station when any of said master stations is in use.

10. In a telephone system, a plurality of telephone stations, a chain of counting relays each corresponding to one of said stations, means associated with each station in a first group of said stations enabling any station in the first group to sequentially operate said counting relays to selectively call another of said stations, means associated with each station in a second group of said stations at other times enabling any station in the second group to directly operate the counting relay corresponding thereto to call a station in the first group, said first means being responsive to an answer by the called station to maintain the counting rela corresponding to the calling station operated independently of said second means.

11. In an intercommunicating system, a plurality of stations each having transmitting and receiving means, each station in a first group of said stations having separate transmitting and receiving circuits at times associated with the transmitting and receiving means thereat, each station in a second group of said stations having separate transmitting and receiving circuits permanently associated with the transmitting and receiving means thereat, conductors common to all of said stations, the transmitting and receiving circuits of the first group of said stations being normally connected to said common conductors in like manner, and means operated by a calling one of said stations in the first group to reverse the connections between said common conductors and the transmitting and receiving circuits of a called station in the first group or to connect the transmitting and receiving circuits of a called station in the second group to said common conductors, whereby two way communication between said calling station and any other one of said stations may be effected over separate and oppositely directed channels.

KENNETH W. GRAYBILL.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 913,607 Zabst Feb. 23, 1909 1,054,176 Corwin Feb. 25, 1913 2,009,405 Leich July 30, 1935 2,324,317 Morris July 13, 1943 

